Field of the Invention
The present invention relates to a processing device, a network device, a control method of a processing device, a control method of a network device, and a recording medium.
The present application claims priority based on Japanese patent application 2016-187491, filed on Sep. 26, 2016 and includes herein by reference the content thereof.
Description of Related Art
In the related art, a distributed control system (DCS) in which field devices such as measurement devices or operation devices called field devices and a control device that controls the field devices are connected through communication means is established in a factory or a plant (hereinafter, referred to as a “plant” in a case where the plant and the factory are commonly termed) such as an industrial plant including a chemical plant, a plant that manages and controls a well site such as a gas field or an oil field or the periphery thereof, a plant that manages and controls generation of hydraulic power, thermal power, or nuclear power, a plant that manages and controls environmental power generation such as solar power and wind power, or a plant that manages and controls a water supply and sewage system or a dam. In such a DCS, an advanced automatic operation is realized.
There are some cases where high reliability and real-time properties are required in a plant system established for realizing an advanced automatic operation described above. For example, feedback control in which a processing result is fed back as an input of the processing and the feedback result is used is often used in control of the plant such as process control. In the feedback control, if a loss occurs in processing data, stability of the control is lowered.
Thus, in the control of the plant, there are some cases where a redundant system which has a redundant configuration using a plurality of devices is used in order to improve availability of the system. For example, the redundant system includes a processing device ordinarily used and another processing device used when it is determined that the processing device is abnormal based on a heartbeat signal (to be described below) from the processing device. The abnormally used processing device is in a standby state and does not perform a control process when the ordinarily used processing device is operated. The ordinarily used processing device outputs the heartbeat signal for notifying that a resource of the processing device is normally operated at predetermined time intervals. The abnormally used processing device monitors the heartbeat signal of the ordinarily used processing device, is switched from the standby state to an active state when the abnormality of the heartbeat signal is detected, and performs the control process instead of the abnormal resource of the ordinarily used processing device (for example, see Japanese Unexamined Patent Application, First Publication No. 2000-218476 or PCT International Publication No. WO2015-098589).
In a control network used in the control of the plant, in order to determine that a communication path between devices connected to the control network is normal, each of the devices broadcasts a diagnostic communication packet which is a packet for diagnosing communication in a fixed cycle. The diagnostic communication packet includes identification information of a transmission source. The device that receives the diagnostic communication packet generates or updates a live list acquired listing the devices which are the transmission sources, and retains information items of the devices capable of communicating (for example, see Japanese Unexamined Patent Application, First Publication No. 2015-092400).
In the system of the related art, it is necessary to add a function (hardware or software) of performing a dedicated process such as a generation process or a reception process of the heartbeat signal in order to establish the redundant system, and device cost may be raised.
For example, even though a resource that provides a process is normal, in a case where the added function is abnormal like in a case where wiring through which the heartbeat signal is transmitted and received is disconnected, the abnormally used processing device detects abnormality of the heartbeat signal, and is switched from the standby state to the active state. Thus, a so-called split-brain syndrome (hereinafter, abbreviated as “SB”) in which data inconsistency due to duplication of the process occurs may occur, and the process may be unstable.
The live list is acquired by listing the devices of which communication states are normal, and is not for use in the redundant system.
One aspect of the present invention provides a processing device, a network device, a control method of a processing device, a control method of a network device, and a recording medium which are capable of realizing a high-stability redundant configuration with low cost.